Hardware Reference
In-Depth Information
Prepare for lift off
The stepper motor is powered by a common lead connected to the power supply and the
other end is connected to a transistor. Since transistors can be used as switches, the leads
of the coil can be grounded alternaively. This alternaive sequence causes the stepper
motor to rotate and the speed of rotaion is controlled by introducing a delay in between
the coil energizaion. The minimum delay required between each energizaion step to make
the stepper rotate properly and avoid misssteps is 2 milliseconds. This is due to the design
limitaions of the stepper motor.
The following table shows the coil energizaion sequence for the stepper motor in a clockwise
direcion (borrowed from the datasheet). The energizaion sequence shown here would make
the stepper rotate in a half step per actuaion, that is, the stepper would rotate 2.8125 degrees
for every actuaion sequence.
It is assumed that you are familiar with stepper motors
and their control theory.
A stepper motor energization sequence from 28BJY-48's datasheet
Engage thrusters
1. Each column in the preceding diagram indicates the lead that needs to be energized
to rotate a single step.
2. For example, in the case of clockwise rotaion, Lead 4 is energized and all other
leads are turned off. The datasheet explains that the stepper motor rotates
approximately 5.625 degrees per step.
3. Hence, 64 actuaion steps are required (
64*5.626 = 360 degrees
) to make one
complete rotaion. The stepper motor is interfaced to a gearbox of 1:64 raio,
and each rotaion takes about 4096 steps.
